1. Field of the Invention
The present invention relates to an image reading technique in a copying machine, a scanner, a facsimile machine and the like, and more particularly to an image reading apparatus which makes occurrence of a black-striped image and a white-striped image due to dirt and the like difficult and, when the black-striped image and the white-striped image are corrected, reduces deterioration of image quality, in case of reading an original sheet as shifting it with a light scanning unit stopped.
2. Related Background Art
Conventionally, in image forming apparatuses such as a copying machine, a scanner, a facsimile machine and the like, an image reading apparatus which has a so-called running reading (or flow scanning) function to read original sheet image information as shifting an original sheet by an automatic original sheet feeding apparatus (called ADF (Auto Document Feeder) hereinafter) in a state that an light scanning unit of irradiating light to the original sheet is being stopped at a predetermined original sheet reading position is known. Here, the ADF is generally provided as an option and structured to be detachable in regard to the main body of the image reading apparatus. In the image reading apparatus, there is a problem that a black stripe or a white stripe occurs (or appears) at a main-scan position of a reading image if dirt or scratch is present on a part of an original sheet glass plate being on an optical path of an image reading unit.
Thus, as a method of eliminating the occurrence of black stripe or white stripe, there is a method of cleaning up the surface of the original sheet glass plate, a method as in Japanese Patent Application Laid-Open No. 2001-144901 of first detecting the occurrence of black stripe or white stripe due to dirt or scratch on the original sheet glass plate and then changing a running reading position according to the detected result, or a method as in Japanese Patent Application Laid-Open No. 2002-77584 of first detecting the occurrence of black stripe or white stripe due to dirt or scratch on the original sheet glass plate and then correcting based on the detected result the values of pixels corresponding to the dirt portion of the reading image by using the values of plural adjacent pixels according to the width of the dirt portion.
However, when the dirt is detected at all the set reading positions, the black stripe or the white stripe occurs even if the reading position is changed. Thus, image quality deteriorates when image data is corrected.